The invention relates to a method for compensating sliding temperature influences on workpieces during a measuring process, in which the workpiece is measured at particular points by scanning with a measuring sensor of a measuring apparatus with respect to the absolute zero point of the latter.
According to the state of the art, in dimensional measurements the temperature of the workpiece is determined before the actual measurement, and the linear thermal expansion is taken into account by means of a coefficient of thermal expansion .alpha. of the workpiece.
For this purpose, according to DE 3,620,118 A1, a gage is placed next to the workpiece. A conclusion can be drawn as to the workpiece temperature from the change in length of the gage. This method is fairly complicated and laborious. The determination of the temperature of the workpiece therefore takes place only once at the start of the measurement run, on the assumption that the temperature does not change or changes only insignificantly during the further measurement run. A corresponding method is employed in DE 3,729,644 A1, except that, in this publication, a temperature sensor is used instead of the gage. In this method too, the temperature is measured only once at the start of the measurement run. The article by Weckenmann A., "Koordinatenmesstechnik im Umbruch" ("Coordinate measurement technique in page make-up") in the German journal: "Technisches Messen tm" ("Technical Measurement tm"), volume 57, 1990, No. 3, pages 95 to 102, also mentions only different stationary temperatures during a measurement run, that is to say the initial temperature of the workpiece is determined for the entire measurement run, in order then to reckon back the workpiece coordinates, for example in relation to a reference temperature of 20.degree. Celsius.
The disadvantage of these methods belonging to the state of the art is that they assume that the temperature of the workpiece does not change during the dimensional measurement. In longer measurement runs at an initial temperature of the workpiece which differs sharply from the ambient temperature, for example after a washing operation at a temperature of, for example, 60.degree. Celsius, however, it cannot be assumed that the temperature of the workpiece remains unchanged, since it decreases sharply during the measurement run. If an unchanged temperature is nevertheless assumed, measuring errors can occur and can be of the same order of magnitude as the total thermal correction, especially when features measured at the start of the measurement run are linked with features measured at the end of the measurement run.